1. Field of the Present Invention
The present invention relates to a method and to an apparatus for controlling advance opening of doors in a twin car elevator.
In particular, the invention relates to the control of advance opening of the doors of the elevator cars of a twin-car elevator, i.e. a so-called double-deck elevator, which are placed one above the other, and the corresponding landing doors.
2. Description of the Related Art
Elevators having two elevator cars placed one above the other in the same car frame are used e.g. in high-rise buildings to increase the transport capacity. Such double-deck elevators may function e.g. as collecting elevators serving only certain floors.
Traditionally, double-deck elevators have had a fixed inter-car distance, as described e.g. in the old German patent specification DE1113293. Controlling the advance opening of doors in double-deck elevators with a fixed inter-car distance is in principle not substantially more difficult than in normal single-car elevators, but double-deck elevators with a fixed inter-car distance, however, involve the problem that in many houses the distances between floors are not mutually equal. Often, especially in modern tall buildings, the entrance hall has a larger height dimension than the other floors. Likewise, the building may contain other special floors of different heights. Moreover, in tall buildings the tolerances may multiply and thus the floor heights of the upper and lower floors may be unequal. In such buildings, only one of the cars in double-deck solutions with a fixed inter-car distance can be driven accurately into position while the other car remains above or below the floor level by an amount corresponding to the difference. This shortcoming is a restriction to the application of double-deck solutions with a fixed inter-car distance.
To solve the above-mentioned problem, double-deck elevators have been developed in which the vertical distance between elevator cars placed in the same car frame, i.e. the inter-floor distance, can be adjusted within suitable limits.
For example, U.S. Pat. No. 5,907,136 discloses a solution where the elevator cars in a car frame are raised or lowered relative to each other and the car frame by means of a lifter and a scissors mechanism provided in the car frame. The car frame is additionally provided with an intermediate beam with a fixing point for the hinge of the scissors mechanism. The upper car is lifted by rotating lifting screws by means of a lifting device, such as a motor provided in the car frame, or by using power cylinders. When the upper car is moving in one direction, the lower car, forced by the scissors mechanism, is simultaneously moving in the other direction.
Similarly, EP specification EP1074503 describes two elevator cars placed one above the other in a car frame which are coupled to be movable by thick threaded bars in relation to each other and the car frame. The threads on the threaded bar moving the upper car are pitched in the opposite sense relative to the threads on the threaded bar moving the lower car, so when threaded bars are rotated, the elevator cars move in opposite directions. The motor driving the threaded bars is disposed in the upper part of the car frame.
In addition, Japanese patent specifications JP2001233553, JP2004010174 and JP2004238189 present double-deck solutions in which the distance between the two elevator cars in the car frame can be adjusted to bring the elevator cars level with different floors.
Although the prior-art solutions referred to above do re-dress the drawback caused by the first-mentioned fixed inter-car distance in double-deck elevators, none of these specifications proposes a solution for controlling the advance opening of the doors of double-deck elevators so as to allow the door opening action to be safely started as early as possible. The problem is typically that the mutual motion and speed of the elevator cars in the car frame relative to the landings are not necessarily the same, because the elevator cars may be moving in different directions relative to the car frame when the elevator is arriving at landings.